Effects of pharmacological and genetic manipulation of glucocorticoids during early development of the zebrafish embryo

Background: The effects of glucocorticoids (GC) on the developing zebrafish embryo (Zfe) are poorly characterised. We have assessed the effects of pharmacological and genetic manipulation of cortisol and glucocorticoid receptors (GR) on global development and stress response during the first 120 hpf. Methods: Cortisol production was modulated by inhibiting the enzyme 11b hydroxylase using morpholino gene knockdown (MO) or incubation in the drug metyrapone (Met) (10 μM). Downstream effects of GC were modulated using the GR agonist dexamethasone (Dex), GR antagonist RU486 or GR knockdown using targeted MO (GR-MO). The effects of these modulations on global development (head–trunk angle, growth-rate and swim bladder inflation), hatch-rate, whole embryo cortisol (WEC) levels, stress response (to stirring) and spontaneous swim behaviour were assessed. Results: Global development was delayed by approximately 8 h following inhibition of GR mediated effects (Ru486 and GR-MO) but accelerated by Dex, this alteration was more apparent in the first 72 hpf with catch-up in growth by 96 hpf. Spontaneous hatching from the chorion was also delayed by inhibition of GR and accelerated by Dex. Inhibition of GR also resulted in altered swim behaviour. Cortisol levels (WEC) increased following stress in control embryos at 72 hpf but not at earlier stages 36 hpf (6.7±0.008 ng/embryo compared to 0.709±0.16 ng/embryo respectively). This rise in WEC could be abolished with Met and MO treatment at 72 hpf but was unaffected at 36 hpf suggesting inactivity of this pathway at earlier developmental stages. Met and MO treated Zfe displayed abnormal post stress swim patterns, with reduced motility following stress compared to controls. Conclusions: Stress response appears to be established in the Zfe by 72 hpf and can be modified by pharmacological and genetic manipulation of GC pathways without impairing global development significantly. These modifications result in altered hatching rates and swim behaviour.